The present invention relates to bio-electric apparatus for cranial electrotherapy stimulation in general and in particular to transcranial electrostimulation (TCES) apparatus for inducing analgesia and similar effects.
It has been demonstrated that non-invasive bio-electric stimulation of certain portions of the brain can achieve analgesic effects. In particular, it has been demonstrated that analgesia can be best effected by stimulation of homeostatic endorphinergic mechanism of the brain structure as described in an article entitled "The anterior pretectal nucleus", by H. Rees and M. H. T. Roberts, Pain Volume 53, No. 2, May 2, 1993. Up to the present time, transcranial electrostimulation has been used to treat acute and chronic pain, such as low back pain, headaches, trigeminal neuralgia, post-herpetic neuralgia, and other disturbed body syndromes.
Reference is also made to an article entitled "Low Frequency Current Density Imaging in Rabbits" by M. L. G. Joy, 1993 Annual Fall Meeting of the Biomedical Engineering Society, Memphis State University, Memphis, Tenn., Oct. 21-24, 1993. Still further, reference is made to an article entitled "The administration of transcranial electric treatment for affective disturbances therapy in alcoholic patients" by E. M. Krupitsky, Drug and Alcohol Dependence, 27 (1991) 1-6, Elsevier Scientific Publishers Ireland Ltd.
It is well known that bio-electric stimulation apparatus is best implemented using current sources rather than voltage sources because treatment regimes are determined in terms of the current required to achieve a particular therapeutic effect. Current sources accommodate for changes in impedance caused, for example, by movements of electrodes on the scalp of a patient, the drying out of gel used as the electrical conducting medium between electrodes and the scalp of a patient, and the like without operator intervention.
The shortest, and therefore the most effective, transcranial path traversing the desired mid-brain portion is between the rear of the scalp of a patient and his forehead as described U.S. Pat. No. 4,140,133 to Kastrubin entitled "Device for Pulse Current Action on Central Nervous System". However, deployment of electrodes across such a transcranial path would require shaving the rear portion of the patient's scalp. Since most patients prefer not to have a portion of their scalp shaved, typically two electrode pairs are employed. Typically, one electrode pair is deployed across a transcranial path extending between a patient's left mastoid area and his forehead and the other electrode pair is deployed across a transcranial path extending between a patient's right mastoid area and his forehead. In this case, the first electrode pair stimulates the left side of the patient's mid-brain and the second electrode pair stimulates the right side of the patient's mid-brain.
Thus, as shown in FIG. 1a, conventional TCES apparatus includes a current source based signal generator providing an electrical signal in the form of square shaped pulses to two electrode pairs detachably attached to a patient's scalp as described above. Furthermore, TCES apparatus includes a control unit having a user interface for setting the average current amplitude of the pulses. The electrical pulses are administered at a frequency of about 77 Hz.
The major disadvantage of conventional TCES apparatus is due to the signal generator being connected in parallel to two electrode pairs. This means that a physician has no control over the individual electrode currents due to different impedances caused by physiological and anatomical differences between the left and right sides of a patient's mid-brain portion, the quality of the conducting medium, and the like. Thus, as can be clearly seen in FIG. 1b, in the present case, the current traversing the right electrode pair is greater than the current traversing the left electrode pair.
The parallel connection also means that there is no control over the division of a pulse traversing the left transcranial path and the right transcranial path. Hence, even through the signal generator provides a square pulse, the fractions of the pulse delivered by the right and left electrode pairs have an indeterminate shape as shown in FIGS. 1b and 1c.
All in all, the design of conventional TCES apparatus often leads a physician to set the current amplitude to too high a setting than is necessary to achieve the desired therapeutic effect. In contradiction to the motivation behind TCES apparatus, it is well known that many patients even complain of burning sensations during treatment sessions!
There is therefore a need for transcranial electrostimulation apparatus (TCES) which overcomes the above-mentioned disadvantages of conventional TCES apparatus.